No matter how hard you try it is still possible to screw up. About all you can do is maximize your odds of doing everything right.
If I were to load for this round again (that will NEVER happen), about the only change I'd made would be switching from a turret press to a progressive. On a progressive you can tell at a glance what step you are at. For example if the bullet is seated at the bullet seating station you know that that has been done and that there is already one charge in the case at the powder station.
I've also firmed up my opinion on small charges. I use to think that those were safe. Now I'm not so sure. Still the 70% rule certainly is an idea (not mine) that will ensure that you don't double up your charges.
My concern about the inherent safety of the 500's, however, continues. At worst a detonation might be possible. At best you've got VERY serious recoil to contend with. Having tried it I'm certainly not going to tempt fate again. I was REALLY lucky this time and I don't want to tempt fate again.